1. Field of the Invention
The invention relates to a dissemination system for satellite broadcasting and related services.
2. Description of the Prior Art
Conventional dissemination systems for satellite broadcasting, as described for example in U.S. Pat. No. 5,787,335, are based on distributing analog high frequency signals by means of coaxial cables. Two cable strands are employed for a simultaneous transmission of signals having two polarizations. An improvement to the above-mentioned system is indicated in U.S. Pat. No. 5,805,975, in which signals of a second polarization are converted to a different frequency region. However, a substantially more broadband cable, and also a more broadband distribution system are needed to realize such an improvement. The problem with arrangements of this kind is that the bandwidth available with conventional cable systems is far less than adequate for distributing all transmittable channels, particularly with simultaneous reception from a plurality of satellites.
Another improvement is provided by receiving systems having controllable terminal stations, as described for example in DE 195 28 589 C1. In these systems, a desired channel is converted, in accordance with a channel selection made by individual subscribers, to an intermediate band that can be transmitted via a coaxial cable. The disadvantage of a solution of this kind is the high complexity of the terminal station, attended by low flexibility. Thus, only receivers which are specially adapted for communication with the terminal station can be employed.
Another approach is made in U.S. Pat. No. 5,995,258. In this approach, a complete optical bus system is described in which the signals received from a satellite are transmitted in a base band. Different optical wavelengths are used for simultaneous transmission of a plurality of polarizations, or for communication in the opposite direction. This system has the disadvantages of an extremely high complexity, a high outlay of optical components, and at the same time a low transmission quality by optical signal transmission in the base band.
A simplified solution to the above approach is represented by U.S. Pat. No. 6,486,907 B1. In this solution, a simplified optical system is described in which the signals are also transmitted in the base band without further modulation. The disadvantage of this arrangement consists of a low transmission quality owing to the optical signal transmission in the base band.